fr=open('letter.txt',mode='r',encoding='utf-8')
plaincode = fr.read()
print('明文:'+plaincode)
print('密文:',end='')
open('letter.txt',mode='r',encoding='utf-8')
for c in plaincode:
print(chr
(ord(c)+3),end='')
fr=open('letter.txt',mode='r',encoding='utf-8')
plaincode = fr.read()
print('明文:'+plaincode)
print('密文:',end='')
open('letter.txt',mode='r',encoding='utf-8')
for c in plaincode:
print(chr
(ord(c)+3),end='')